This invention relates generally to arrangements for controlling and adjusting deflection units, and more particularly, to a system which automatically adjusts the characteristics of the deflection unit with respect to its coordinate origin and the slope of the deflection function.
The use of deflection units is required, for example, to adjust deflection mirrors for the laser beams in laser recording equipments. In such systems, a position signal is sensed by an actual-value measuring circuit and compared against a reference value. A controller which controls the deflection unit brings the position signal into agreement with the reference value. It is a problem with such systems, however, that the actual-value measuring circuits which are commonly used are of a type which operates with a capacitive sensor which is subject to thermal drift which produces a deviation between the preset reference value and the actual position of the deflection mirror. Such a deviation produces displacements and scale changes in the recording field. The temperature drift produces not only a shift in the origin of the characteristic, but also a change in its slope.
Prior art systems embodied in commercially available equipments compensate for the temperature drift by preheating the deflection units and requiring the performance of a manual compensation procedure. This is generally achieved in the controller by the manipulation of potentiometers which adjust the characteristic. It is a problem, however, that complete compensation is not possible by preheating the deflection unit. With the manual compensation procedure, a correction of the error produced by the thermal drift is generally possible only for a given operating temperature.
An arrangement for controlling the upper and lower limits of a position control system is described in "Patent Abstracts of Japan," June 9, 1981, vol. 5, no. 88, 56-35222. In this known arrangement, a position measuring signal produced by a position pickup is conducted via a differential amplifier and a multiplier. The position measuring signals for the upper and lower limits are stored in a memory. The memory for the lower limit controls the zero point of the differential amplifier by means of an arithmetic unit. A multiplication factor for the multiplier is set via a further arithmetic unit in response to the difference between the two limits. In this manner, fast control is achieved independently of the changes in the upper and lower limits. Although this known arrangement achieves an adaptation to the limits of a control system, the automatic adjustment of a characteristic which is desired for a deflection unit is not achieved.
It is, therefore, an object of the invention to provide an arrangement for adjusting the linear characteristic of deflection unit so that automatic adjustment is achieved.